1. FIELD OF THE INVENTION
The present invention relates to a voltage regulator for an alternator of a vehicle.
2. DESCRIPTION OF THE PRIOR ART
The voltage regulator of the type described above always maintains an output voltage of the alternator to a preset voltage by increasing or decreasing an electric current flowing through its rotor coil responsive to the variation of the electric load of the alternator. The increase or decrease in electric current is performed by changing the duty ratio of switching means in accordance with the difference between the output voltage and the preset voltage, for example.
When the electric load of the alternator is rapidly increased, the voltage regulator increases the electric current flowing through the rotor coil so as to maintain the output voltage of the alternator constant. This results in an engine which rotates the alternator being overloaded, and particularly at an engine idling time when the rotating torque is small, the number of revolutions of the engine being decreased to incur engine stall.
U.S. Pat. No. 4,459,489 proposes a voltage regulation device by which the electric current flowing through the rotor coil of the alternator is gradually varied to prevent the engine stall when the electric current is rapidly changed.
And recently, an idle speed control (ISC) device has been also employed for temporally increasing the amount of the fuel supply to maintain th number of revolutions of the engine at a constant level when it begins to lower.
However, vehicles provided with the above described voltage regulation device or ISC device have problems that when an intermittent load such as a wiper motor is connected to an alternator, the accompanied periodical variation of the engine load cannot be timely regulated due to the delay time in the control system and accordingly, the number of revolutions of an engine is varied on such a comparatively large scale to generate vibrations. Such vibrations are transmitted to the interior of a vehicle room to worsen the comfartable ride.